What absorbs at 3642 cm⁻¹ in an FTIR spectrum?
A band near 3642 cm⁻¹ can point to several functional groups. Below are the most likely assignments, ranked by how much published evidence supports each — every one traceable to literature (DOI) and cross-validated against our 130,000+ reference spectra and knowledge graph.
Backed by 8 cited sources
Quick answer
A band near 3642 cm⁻¹ is usually interpreted by checking which functional groups repeatedly co-occur there in the literature, then confirming at least one or two additional peaks in the same sample. This page ranks those assignments by accumulated evidence rather than by a single fixed textbook rule.
Possible functional-group assignments
| Functional group | Supporting facts | Cited sources | Top confidence |
|---|---|---|---|
| Hydroxyl (O-H) | 12 | 12 | 1.0 |
| Water (H2O) | 3 | 3 | 1.0 |
| Metal hydroxyl | 1 | 1 | 1.0 |
| Hydrogen bond | 1 | 1 | 1.0 |
| Silanol (Si-OH) | 1 | 1 | 0.8 |
Ranking reflects accumulated literature evidence, not a single fixed rule. Always confirm against your sample context.
Possible materials
| Material | Supporting peaks | Overlapping groups | Cited sources |
|---|---|---|---|
| Silica | 3642, 1100, 1080 | Hydroxyl (O-H) | 1 |
| H2O | 3642, 1076, 1450 | Hydroxyl (O-H), Water (H2O) | 1 |
| hydroxyapatite | 3642, 1620, 1639 | Hydroxyl (O-H) | 1 |
| water | 3642, 1018, 2945 | Hydroxyl (O-H), Water (H2O) | 1 |
| TiO2 | 3642, 1700, 1093 | Hydroxyl (O-H) | 1 |
Materials are shown only when the same literature pool supports this band and at least one additional characteristic peak.
Spectrum logic
This band becomes meaningful only when read with its neighboring peaks. In practice, analysts first look at the assignments above, then check whether the same sample also shows other peaks expected for the same structural motif. A lone band near 3642 cm⁻¹ is usually not enough for material identification by itself.
Real-world usage
This type of query is common in polymer identification, unknown plastic screening, QC troubleshooting, recycled-material verification, and literature-backed peak assignment review.
Common mistakes
- Treating one isolated band as proof of a material without checking at least one or two supporting peaks.
- Ignoring overlap: multiple functional groups can contribute near the same wavenumber.
- Skipping validation when additives, blends, oxidation, or contamination may distort the spectrum.
Verification advice
When ambiguity remains, validate the hypothesis with DSC, GC-MS, or TGA, especially for blends, degraded samples, and filled polymers.
Literature behind these assignments
-
Hydroxyl (O-H) confidence 1.0
“2500 2512.6 2523.3 2513.2 - 2512.9 2513.2 - - 3287.1 3409.3 3419.5 3434.8 3541.7 3444.9 3470.4 3530 Due to O-H stretching in water - - 3642.5 3642.4 -”
Theoretical and experimental study of structures and properties of cement paste The nanostructural aspects of C–S–H DOI: 10.1016/j.jpcs.2011.05.001 -
Hydroxyl (O-H) confidence 1.0
“(cm(cid:1)1) Peaks Stretching Functional group 3641.60 OH vibration Hydroxyl group 3568.31 OH Stretching Hydroxyl group”
Spectral characterization of hydroxyapatite extracted from Black Sumatra and Fighting cock bone samples: A comparative analysis DOI: 10.1016/j.sjbs.2020.11.020 -
Hydroxyl (O-H) confidence 1.0
“The five vibrational features occur at 1030 cm1 (Si-F in gas phase SiF4), 1076 cm1 (Si-O in SiO2 film), 1728 cm1 (H2O scissors mode of adsorbed water), 3482 cm1 (O-H stretch of adsorbed H2O), and 3642 (SiO-H in surface silanol groups or H-X”
Montano-Miranda 和 Muscat - 2003 - Gas-phase HFvapor etching of thermal silicon diox DOI: 10.4028/www.scientific.net/SSP.92.207 -
confidence 1.0
“Explicit assignment: 'narrow band of free hydroxyl group of calcium hydroxide at 3642 cm-1'”
Abu Zeid 等 - 2017 - Chemistry and Bioactivity of NeoMTA Plus (TM) vers DOI: 10.1155/2017/8736428 -
Hydroxyl (O-H) confidence 1.0
“Assignment6,21-23 Peaks Vibration 3642 OH stretching Bridging OH in TiO 2 3432, 3238 OH stretching”
Almeida 等 - 2011 - Photo-catalytic oxidation of cyclohexane over TiO2 DOI: 10.1039/c0cp00879f -
Hydroxyl (O-H) confidence 1.0
“cm-1 whilst particular antisymmetric stretching vibrations modes of water manifest at around manifest at around 3489 The sharp peak at 3642 belonging to Ca-OH stretching 3489 cm-1.”
Phase Composition of Silica Fume—Portland Cement Systems Formed under Hydrothermal Curing Evaluated by FTIR, XRD, and TGA DOI: 10.3390/ma14112786 -
Hydroxyl (O-H) confidence 1.0
“OH stretch 3642 Primary alcohol curonic acid content in a considerable amount and a low content of proteins.”
Maher 等 - 2021 - Optimization of Ultrasound-Assisted Extraction of DOI: 10.3390/antiox10101612 -
Water (H2O) confidence 1.0
“M 216O/H 218O situ H exchange experiments, Garczarek and Gerwert (37) also detected a water a cm-1 n vibrational band at 3642 in the initial state, which has been identified as arising from a u water molecule that is hydrogen bonded to depr”
Morgan 等 - 2007 - Water structural changes in the L and M photocycle DOI: 10.1021/bi0616596.
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